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鲁安怀,李艳,丁竑瑞,王长秋. 2019. 地表“矿物膜”:地球“新圈层”. 岩石学报, 35(1): 119-128
地表“矿物膜”:地球“新圈层”
作者单位
鲁安怀 北京大学地球与空间科学学院, 造山带与地壳演化教育部重点实验室, 矿物环境功能北京市重点实验室, 北京 100871 
李艳 北京大学地球与空间科学学院, 造山带与地壳演化教育部重点实验室, 矿物环境功能北京市重点实验室, 北京 100871 
丁竑瑞 北京大学地球与空间科学学院, 造山带与地壳演化教育部重点实验室, 矿物环境功能北京市重点实验室, 北京 100871 
王长秋 北京大学地球与空间科学学院, 造山带与地壳演化教育部重点实验室, 矿物环境功能北京市重点实验室, 北京 100871 
基金项目:本文受科技部"973"项目(2007CB815600、2014CB846000)及国家自然科学基金重点项目(41230103、91851208)、国际合作重点项目(41820104003)、优秀青年基金项目(41522201)和面上项目(41872042)联合资助.
摘要:
      地球表层是一个极为复杂的开放系统,其中所充满的阳光、大气、水分、有机酸、无机酸/盐、矿物质和微生物等彼此之间无时无刻不在发生着人们尚未充分认识到的多种自然作用。本文采用环境矿物学、半导体物理学与光电化学等交叉学科研究手段,在我国南方红壤、西南喀斯特和西北戈壁等典型陆地生境中,发现直接暴露于太阳光下的土壤/岩石表面广泛发育有几十纳米到数百微米厚度的铁锰氧化物"矿物膜";详细研究了铁锰氧化物"矿物膜"中矿物组成及其精细结构特征,发现半导体性能优异的水钠锰矿普遍存在,其晶体结构中富含促进其光催化功能的稀土元素Ce。在这些生境中,矿物岩石表面所包覆的铁锰氧化物"矿物膜"总是朝着太阳光发育,岩石背面却不出现"矿物膜",揭示出太阳光照射下的地球陆地表面普遍存在的"矿物膜"与太阳光有着直接的响应关系。光电化学测试结果显示,天然"矿物膜"具有较好的日光响应性能,由其制成的电极在可见光照射下皆能产生明显的光电流,而不含铁锰氧化物矿物的岩石基质样品及石英、长石等矿物样品几乎不产生光电流,表明"矿物膜"光电流的产生主要与铁锰氧化物有关。进一步测得"矿物膜"中主要铁锰氧化物的禁带宽度均小于2.5eV,证明其均为对可见光具有广泛而良好吸收的天然半导体矿物。以全球日光平均辐照强度100mW/cm2计以及全球典型生境中"矿物膜"分布面积估算,全球"矿物膜"吸收太阳能等效为生物质能的最大量与2017年度全球糖类产量(1.92亿吨)相当。铁锰氧化物"矿物膜"不仅存在于陆地地表,还存在于海洋透光层中。可以认为地表"矿物膜"是地球上分布最广的天然"太阳能薄膜",从功能上"矿物膜"相当于继地核、地幔和地壳之后的地球第四大圈层,事实上构成了地球"新圈层",也是地球在太阳光能量驱动下发生外营力地质作用的关键地带。在此基础上,本文提出从"矿物膜"中产生的矿物光电子与太阳光子和元素价电子共同组成了地表存在的三种主要能量形式的认识。深入探讨太阳光照射下地表多圈层交互作用界面上所发生的电子传递与能量转化的微观机制,有助于深刻理解地表"矿物膜"这一地球"新圈层"如何影响地球物质演化、生命起源进化与环境变化演变的宏观过程。
英文摘要:
      The terrestrial system on Earth surface is a very complicated open system, where the sunlight, air, water, organic acids, inorganic acids/salts, minerals and microorganisms are always closely interacting with each other. And these natural interactions still await further scientific investigations. Based on the cross-field research methods of environmental mineralogy, semiconducting physics and photoelectron-chemistry, this study revealed a ferromanganese "mineral membrane" widely developed on rock and soil surfaces and directly exposed under sunlight, in such various typical terrestrial environments as Gobi desert, karst regions and red soils areas. This "mineral membrane" is usually of several tens of nanometer to hundreds of micrometer in thickness. The fine structural characteristics of the Mn oxides in "mineral membrane" were investigated, and the prevalent existence of layered-type birnessite was proved. Besides, the rare earth element Ce was found to be structurally-correlated with birnessite in "mineral membrane", which could promote its semiconducting function. The "mineral membrane" is always developed on the surface sides of rocks rather than the reverse sides, indicating a direct correspondence with sunlight exposure. As revealed by photoelectron-chemistry experiments, electrodes made of natural "mineral membrane" powders could generate remarkable photocurrents under illumination of visible light, whereas the rock substrates and quartz and feldspar minerals could barely achieve that. These results indicated the generation of photocurrent was mainly due to the Fe- and Mn-oxides. Further measurements showed the bandgap of main Fe- and Mn-oxides in "mineral membrane" are all below 2.5eV, suggesting they are all visible light responsive semiconducting minerals. Based on the worldwide average solar irradiation intensity of 100mW/cm2 and the global distribution areas of "mineral membrane", it was estimated that the energy mass of solar energy converted to biomass energy by "mineral membrane" could parallel with the global sugar production of the year 2017 (192 million tons). Last but not least, the ferromanganese "mineral membrane" not only spreads on land surface but also reaches out to the marine euphotic zones. "Mineral membrane" of the Earth surface functions as the fourth great layer section, named here "new sphere" of the Earth, following the earth's core, mantle and crust, and as the critical zone promoting external-power geological processes under solar irradiation. We therefore proposed that the three main energy forms on Earth surface as photoelectrons from "mineral membrane", solar photons and valence electrons of elements. The photoelectrons from "mineral membrane" can participate varieties of biogeochemical processes, and make a ubiquitous and profound impact on the matter cycling on planets' surface.
关键词:地表"矿物膜"  水钠锰矿  元素Ce  矿物光电子  地球"新圈层"
投稿时间:2018-08-08  修订日期:2018-11-12
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